Identification of microplastic and microbial compositions in a wastewater treatment plant employing RBC unit

This study investigates the abundance, characteristics, removal efficiency, and microbial colonization of microplastics (MPs) in a full-scale wastewater treatment plant (WWTP) employing Rotating Biological Contactor (RBC), an attached-growth technology for biological treatment. Wastewater and sludge samples were collected in three seasons (winter, spring, and summer), and a total of 6,160 suspected particles were isolated. Fibers were consistently the dominant morphology across all sampling points and seasons, accounting for 92% of all extracted particles. Seasonal variations were observed in influent concentrations, with the highest MP loads measured during winter and summer, likely corresponding to fluctuations in campus-related human activity patterns. Despite these variations, effluent concentrations remained low (12–14 particles/L), and overall removal efficiencies ranged between 92% and 96%. Sludge was identified as the major sink for MPs, containing 102–132 particles/g. Size-based evaluations revealed that medium-sized particles (250–1000 µm) were the predominant class and were removed more effectively than other fractions. Raman spectroscopy identified polyethylene terephthalate, polyvinyl chloride, nylon, and polypropylene as the most common polymer types. To assess microbial community structure, 16S rRNA gene sequencing was applied to both bulk samples and microplastic-associated fractions collected in November 2024 and February 2025. The dominant bacterial phyla across all samples were Proteobacteria, Firmicutes, Bacteroidetes, and Chloroflexi, although their relative abundances varied by sampling point and date. MP-associated microbial assemblages differed from the surrounding bulk communities, reflecting selective colonization processes on microplastic surfaces.